feat: implement ecosystem contract and prepare v2.2.0

[Foscat]

Summary

• implement the reviewed three-library ecosystem ownership, manifest, compatibility, semantic component, and shared-token contracts
• prepare UI Style Kit CSS 2.2.0 while retaining all 89 exports and all 11 documented deprecations
• pin the published Interactive Surface 1.6.0 and Layout Style 3.0.1 merge commits
• set the npm homepage to the live GitHub Pages demo: https://foscat.github.io/ui-style-kit-css/
• enforce strict default registry verification and explicit UI-candidate mode in every release workflow

Verification

• TDD RED/GREEN/mutation coverage for release metadata, immutable companion pins, workflow policy, and npm dry-run propagation
• 131/131 unit and contract tests
• 147/147 Playwright E2E cases across Chromium, Firefox, and WebKit
• 9/9 Axe checks; 33/33 curated visual checks
• 990/990 preset/theme/mode/browser matrix
• current and minimum seven-scenario ecosystem matrices; 7/7 clean-install combinations
• independent code review and focused re-review: zero findings
• npm pack/publish dry-run: 49 files, 89 exports
• full and production-only audits: 0 vulnerabilities

Compatibility

• minimum: ui-style-kit-css 2.1.0, interactive-surface-css 1.5.0, layout-style-css 3.0.0
• current: ui-style-kit-css 2.2.0, interactive-surface-css 1.6.0, layout-style-css 3.0.1
• SemVer impact: additive minor release; no export removals or major-version break